[rabbitmq-discuss] BasicPublish() from .NET client hangs after upgrading server to 1.7.1

Thu Jan 28 16:34:30 GMT 2010

On Thu, Jan 28, 2010 at 04:04:43PM +0000, Matthew Sackman wrote:
> We shall investigate further. Many thanks for your help,

Yup, it's a bug in win32sysinfo.c which Erlang uses to call Windows to
find out how much memory it has. It has the following code:

void get_avail_mem_ext() {
    char answer[512];
    MEMORYSTATUSEX ms;
    ms.dwLength=sizeof(MEMORYSTATUSEX);
    GlobalMemoryStatusEx(&ms);
    sprintf(answer,"%d %I64d %I64d %I64d %I64d %I64d %I64d\n",
	    ms.dwMemoryLoad,
	    ms.ullTotalPhys,
	    ms.ullAvailPhys,
	    ms.ullTotalPageFile,
	    ms.ullAvailPageFile,
	    ms.ullTotalVirtual,
	    ms.ullAvailVirtual
	    );
    return_answer(answer);
    /*    
	DWORD     dwLength;
	DWORD     dwMemoryLoad;
	DWORDLONG ullTotalPhys;
	DWORDLONG ullAvailPhys;
	DWORDLONG ullTotalPageFile;
	DWORDLONG ullAvailPageFile;
	DWORDLONG ullTotalVirtual;
	DWORDLONG ullAvailVirtual;
    */
}

Sadly, whoever wrote that didn't notice the fact that DWORD and DWORDLONG
are unsigned, whereas %I64d says to interpret the value as signed.

$ cat foo.c
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

main()
{
  uint64_t n = 4293308416;
  printf("%I64d\n", n);
  printf("%I64u\n", n);
  return 0;
}

$ gcc -o foo foo.c && ./foo 
                                                        -1658880
                                                      4293308416

This is exactly what is happening. We'll file a bug with the erlang
people and try and work around it. I don't suppose by any chance you're
compiling erlang from source under Windows are you?

Best wishes,

Matthew